The present invention relates to processing of cellulose, and more particularly, to fiber opening and downstream processing and chemistry.
The functionalization of cellulose from sheet and roll forms generally begins with an opening step to prepare the fibers for downstream processing and chemistry. In the context of downstream acetylation to prepare various cellulose acetate products, in particular, cellulose is often sourced from hardwood and softwood pulps and cotton linters.
Several factors introduce limitations at various stages in cellulose processing. Sheet hardness is one such factor that can influence the fiber opening. For example, employing standard attrition equipment used in the art, a hardness index of a pulp feed should be less than about 3 psi/mil. The Mullen burst test, which measures the pressure required to puncture a cellulose sheet or paperboard as a function of its load carrying capacity under specific conditions, also provides an indication of whether the cellulose feed will perform well in the equipment.
It has been indicated that the fiber-opening step can be improved using polar liquids, in particular water. While water is well suited for the fiber-opening step, especially in view of concerns for providing green chemical processes, its presence in the milled pulp product can impede downstream chemistries. For example, in the acetylation process, water can consume the acetylation reagent acetic anhydride, leading to inefficient consumption of this reagent. Attempts to improve processing for downstream chemistries have led to milled products lacking consistent and reliable moisture content. Drying attempts often lead to under dried, over dried, or unevenly dried product, which influences quality of product at the functionalization stage.